The present invention relates to drafting instruments and aids such as rulers or scales and more particularly to a novel magnifier for use with an engineer's scale to facilitate visual perception of scale markings.
In preparing engineering or working plans and drawings for the construction or fabrication of machinery, buildings, and technical products, it is necessary to prepare detailed, precise renditions according to a predetermined scale. The preparation of such plans and drawings necessarily requires sophisticated drafting techniques utilizing scales and other instruments. A particularly valuable instrument is a so-called engineer's scale which is also known as a triangular scale. Triangular scales include three elongate triangular portions which are radially opposed from one another with each portion having opposed, different indicia or scale markings. Three elongate grooves extend along the length of the triangular scale to permit gripping by a draftsman's fingers for shifting the scale, rotating it about its longitudinal axis to dispose selected scale markings adjacent a workpiece, etc.
It can be appreciated that accurate reading of the scale markings on a triangular scale is necessary in order to properly lay out plans or drawings. Because the scale markings generally are quite small, it is often difficult for a draftsman to accurately perceive markings and locate a pencil or pen adjacent a selected marking during the drawing process. In recognition of this problem several prior art proposals have been made to mount verniers or magnifying instruments on a triangular scale in order to facilitate viewing of the scale markings. Such prior art proposals directed to magnifiers are defective from several standpoints. Primarily, know magnifiers generally permit magnification of only a selected scale and it is necessary to remove the magnifier and locate it on a different position of the scale in order to view different scale markings. Additionally, known scale magnifiers generally do not permit ready adjustability of the magnifier in order to compensate for different visual acuity of draftsmen.
Accordingly, it is a general object of the present invention to provide a magnifier for facilitating visual perception of scale markings on a scale, such as a triangular scale, which includes a magnifying element which is supported above the scale by a mounting means. The mounting means includes pivot means for permitting selective tilting of the magnifying element about a pivot axis extending generally parallel to the longitudinal axis of the scale. The magnifying element overlaps the apex of an upwardly disposed triangular portion of the scale so that upon selective tilting, a draftsman may view a selected one of the scales which is disposed adjacent the workpiece.
Another object of the present invention is to provide a magnifier, as described above, in which the mounting means is mounted on the scale in a manner to permit manual shifting in reciprocal directions generally paralleling the longitudinal axis of the scale. The pivot means, mentioned with respect to pivotally mounting the magnifying element to the mounting means, is positioned for locating the pivot axis above the scale.
Still another object of the present invention is to provide a magnifier, as described above, in which the mounting means includes runner means formed for being slideably received in at least one of the longitudinal grooves of the scale. Extending from the runner means is at least one extension or leg means to which the magnifying element is pivotally connected.
These and additional objects and advantages of the present invention will be more readily understood and appreciated after a consideration of the drawings and the following detailed description of the preferred embodiment.